MAX989 Maxim, MAX989 Datasheet - Page 8

• Manufacturer Part Number: MAX989
• Description: The MAX985/MAX986/MAX989/MAX990/MAX993/MAX994 single/dual/quad micropower comparators feature low-voltage operation and rail-to-rail inputs and outputs
• Manufacturer: Maxim

Micropower, Low-Voltage, UCSP/SC70,
Rail-to-Rail I/O Comparators
5) Calculate R2 as follows. For this example, choose an
6) Verify trip voltages and hysteresis as follows:
The MAX986/MAX990/MAX994 have ±3mV internal
hysteresis. They have open-drain outputs and require
an external pullup resistor (Figure 2). Additional hys-
teresis can be generated using positive feedback, but
the formulas differ slightly from those of the
MAX985/MAX989/MAX993.
Figure 2. Additional Hysteresis (MAX986/MAX990/MAX994)
8
Hysteresis
V rising: V
V falling
R2 =
R2 =
IN
IN
8.2kΩ standard value:
_______________________________________________________________________________________
V
IN
⎛
⎜
⎝
⎛
⎜
⎝
1.2 x 12k
V
:
R1
REF
V
=
V
3.0V
THR
THF
THR
V
x R
THR
= V
=
R2
Ω
1
V
V
⎞
⎟ −
⎠
⎞
⎟ −
⎠
REF
REF
−
1
THR
V
1
THF
12
R3
x R1 x
R
1
−
1
1
k
MAX986/MAX990/MAX994
Ω
⎛
⎜
⎝
V
V
−
V
R x V
CC
EE
CC
1
−
R
⎛
⎜
⎝
MAX986
MAX990
MAX994
1
R1
R
3
1
2 2
3
.
OUT
CC
+
1
M
Ω
R
⎞
⎟
⎠
1
2
=
+
R4
8 03
R
1
.
3
⎞
⎟
⎠
k
Ω
Use the following procedure to calculate resistor
values:
1) Select R3 according to the formulas R3 = V
2) Choose the hysteresis band required (V
3) Calculate R1 according to the following equation:
4) Choose the trip point for V
5) Calculate R2 as follows:
6) Verify trip voltages and hysteresis as follows:
Power-supply bypass capacitors are not typically need-
ed, but use 100nF bypass capacitors when supply
impedance is high, when supply leads are long,
or when excessive noise is expected on the supply
lines. Minimize signal trace lengths to reduce stray
capacitance.
Hysteresis
V rising: V
V falling
500µA or R3 = (V
smaller of the two resulting resistor values.
example, choose 50mV.
the trip point for V
voltage at which the comparator switches its output
from low to high as V
IN
IN
R2 =
R1 = (R3 + R4) x (V
:
⎛
⎜
⎝
V
=
THR
⎛
⎜
⎝
R1
THF
1
V
V
REF
THR
+
Board Layout and Bypassing
V
= V
=
THR
REF
R
1
V
IN
x R
2
REF
−
THR
IN
+
falling). This is the threshold
V
- V
1
rises above the trip point.
THF
⎞
⎟ −
⎠
x R1 x
R
−
CC
3
⎛
⎜
⎝
1
IN
) / 500µA - R4. Use the
HB
1
+
R x V
R
R
1
1
R
1
3
rising (V
/ V
4
−
+
⎞
⎟
⎠
CC
R
CC
R
4
)
3
⎞
⎟
⎠
THR
1
+
HB
R
). For this
4
; V
THF
REF
is
/